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JQuery has a neat function that allows us to read external and local JSON files.

jQuery.getJSON( url, [data], [callback] )

The first parameter of this function, the URL you are planning to read, is required. The second parameter is used if you need to POST data to the URL. Last but no least, the callback function, although not required, is almost always necessary.

Important: The URL can be to a local or external file. If the file is in another server the URL must contain a callback variable. You’ll see how this works in the next paragraphs.

The Json File

Rather than making my own JSON file, like I’ve done for previous XML and JSON tutorials, I’ve decided that we’ll use Twitter’s search API this time.

Twitter’s search API has many different search options, but you only need to know about the callback and query “q” options.

Most basic Twitter search URL.

http://search.twitter.com/search.json?callback=foo&q=google+wave

Although required in the URL, your script does not have to have a callback function or variable. Just give the callback a value of “?” like this.

http://search.twitter.com/search.json?callback=?&q=google+wave

Important: Different APIs have different callback URL names, flickr’s API for example uses “jsoncallback” instead of “callback” in the URL. Always read the API docs very carefully.

Now that you know what it takes to query Twitter, take a look a sample response.

$(document).ready(function(){
// twitter api's base url
var url="http://search.twitter.com/search.json?callback=?&q=";
// we'll store the search term here
var query;
// when the user clicks the button
$("button").click(function(){
// get value in the search box and store it in the variable
query=$("#query").val();
// get the json file
});
});

Okay, we have the basic set up, it’s now time to build the getJSON part.

Our URL parameter will be the URL concatenated with the query (url+query). Since we are not posting data we don’t need the second parameter. The function getJSON returns a JSON object which we will use as parameter for the callback function.

// get the json file
$.getJSON(url+query,function(json){
// this is where we can loop through the results in the json object
});

Looping Through The Results

Notice that we passed an object called “json” to the callback function, you can change the name of this object but I think json makes sense. This object now contains all the json data we need, all we need to to now is loop through the results sent from twitter.

// this is where we can loop through the results in the json object
$.each(json.results, function(i,tweet){
// this is where we do what we want with the tweet
});

Let’s break down the loop. the first parameter “json.results” refers to the array in the object we want to loop through, since the only array in the json response from the Twitter search API is “results” we say json.results. The second parameter, the function, has two parameters and you can change the name of them if you want to, I used “i” and “tweet”.

The the “i” refers to the current number of loops and you could use if for example to display the number of results you got from the query. The “tweet” refers to the current tweet, so you can refer to any of the following keys by prepending the word “tweet” before them.

To get the username from which the tweet originated you would use tweet.from_user , to get the actual tweet you would use tweet.text.

Let’s put the profile image and tweet in our div tag.

// this is where we can loop through the results in the json object
$.each(json.results,function(i,tweet){
// this is where we do what we want with each tweet
$("#results").append('<p><img src="'+tweet.profile_image_url+'" widt="48" height="48" />'+tweet.text+'</p>');
});

This article is part of the ‘Porting PHP to Javascript’ Project, which aims to decrease the gap between developing for PHP & Javascript.

A lot of people are familiar with PHP’s functions, and though Javascript functions are often quite similar, some functions may be missing or addressed differently. The Javascript implementations should be as compliant with the PHP versions as possible, a good indication is that the PHP function manual could also apply to the Javascript version.

Porting crucial PHP functions to Javascript can be fun & useful. Currently some PHP functions have been added, but readers are encouraged to contribute and improve functions by adding comments. Eventually the goal is to save all the functions in one php.js file and make it publicly available for your coding pleasure.

Speed Up Your Javascript Load Time

Javascript is becoming increasingly popular on websites, from loading dynamic data via AJAX to adding special effects to your page.

Unfortunately, these features come at a price: you must often rely on heavy Javascript libraries that can add dozens or even hundreds of kilobytes to your page.

Users hate waiting, so here are a few techniques you can use to trim down your sites.

Find The Flab

Like any optimization technique, it helps to measure and figure out what parts are taking the longest. You might find that your images and HTML outweigh your scripts. Here’s a few ways to investigate:

1. The Firefox web-developer toolbar lets you see a breakdown of file sizes for a page (Right Click > Web Developer > Information > View Document Size). Look at the breakdown and see what is eating the majority if your bandwidth, and which files:

2. The Firebug Plugin also shows a breakdown of files – just go to the “Net” tab. You can also filter by file type:

3. OctaGate SiteTimer gives a clean, online chart of how long each file takes to download:

Disgusted by the bloat? Decided your javascript needs to go? Let’s do it.

Compress Your Javascript

First, you can try to make the javascript file smaller itself. There are lots of utilities to “crunch” your files by removing whitespace and comments.

You can do this, but these tools can be finnicky and may make unwanted changes if your code isn’t formatted properly. Here’s what you can do:

2. Use Rhinoto compress your javascript. There are some online packers, but Rhino actually analyzes your source code so it has a low chance of changing it as it compresses, and it is scriptable.

Install Rhino (it requires Java), then run it from the command-line:

java -jar custom_rhino.jar -c myfile.js > myfile.js.packed 2>&1

This compresses myfile.js and spits it out into myfile.js.packed. Rhino will remove spaces, comments and shorten variable names where appropriate. The “2>&1″ part means “redirect standard error to the same location as the output”, so you’ll see any error messages inside the packed file itself (cool, eh? Learn more here.).

Using Rhino, I pack the original javascript and deploy the packed version to my website.

Debugging Compressed Javascript

Debugging compressed Javascript can be really difficult. I suggest creating a “debug” version of your page that references the original files. Once you test it and get the page working, pack it, test the packed version, and then deploy.

If you have a unit testing framework like jsunit, it shouldn’t be hard to test the packed version.

Eliminating Tedium

Because typing these commands over and over can be tedious, you’ll probably want to create a script to run the packing commands. This .bat file will compress every .js file and create .js.packed:

Of course, you can use a better language like perl or bash to make this suit your needs.

Optimize Javascript Placement

Place your javascript at the end of your HTML file if possible. Notice how Google analytics and other stat tracking software wants to be right before the closing </body> tag.

This allows the majority of page content (like images, tables, text) to be loaded and rendered first. The user sees content loading, so the page looks responsive. At this point, the heavy javascripts can begin loading near the end.

I used to have all my javascript crammed into the <head> section, but this was unnecessary. Only core files that are absolutely needed in the beginning of the page load should be there. The rest, like cool menu effects, transitions, etc. can be loaded later. You want the page to appear responsive (i.e., something is loading) up front.

Load Javascript On-Demand

An AJAX pattern is to load javascript dynamically, or when the user runs a feature that requires your script. You can load an arbitrary javascript file
from any domain using the following import function:

function $import(src){

var scriptElem = document.createElement('script');

scriptElem.setAttribute('src',src);

scriptElem.setAttribute('type','text/javascript');

document.getElementsByTagName('head')[0].appendChild(scriptElem);

}

// import with a random query parameter to avoid caching

function $importNoCache(src){

var ms = new Date().getTime().toString();

var seed = "?" + ms;

$import(src + seed);

}

The function $import(‘http://example.com/myfile.js’) will add an element to the head of your document, just like including the file directly. The $importNoCache version adds a timestamp to the request to force your browser to get a new copy.

To test whether a file has fully loaded, you can do something like

if (myfunction){

// loaded

}

else{ // not loaded yet

$import('http://www.example.com/myfile.js');

}

There is an AJAX version as well but I prefer this one because it is simpler and works for files in any domain.

Delay Your Javascript

Rather than loading your javascript on-demand (which can cause a gap), load your script in the background, after a delay. Use something like

var delay = 5;

setTimeout("loadExtraFiles();", delay * 1000);

This will call loadExtraFiles() after 5 seconds, which should load the files you need (using $import). You can even have a function at the end of these imported files that does whatever initialization is needed (or calls an existing function to do the initialization).

The benefit of this is that you still get a fast initial page load, and users don’t have a pause when they want to use advanced features.

In the case of InstaCalc, there are heavy charting libraries that aren’t used that often. I’m currently testing a method to delay chart loading by a few seconds while the core functionality remains available from the beginning. You may need to refactor your code to deal with delayed loading of components. Some ideas are to use SetTimeout to poll the loading status periodically, or having a function called at the end of your included script to tell the main program the script has been loaded.

Cache Your Files

Another approach is to explicitly set the browser’s cache expiration. In order to do this, you’ll need access to PHP so you can send back certain headers.

In this case, the cache will expire in (60 * 60 * 24 * 3) seconds or 3 days. Be careful with using this for your own files, especially if they are under development. I’d suggest caching library files that you won’t change often.

If you accidentally cache something for too long, you can use the $importNoCache trick to add a datestamp like “myfile.js?123456″ to your request (which is ignored). Because the filename is different, the browser will request a new version.

Setting the browser cache doesn’t speed up the initial download, but can help if your site references the same files
/> on multiple pages, or for repeat visitors.

Combine Your Files

A great method I initially forgot is merging several javascript files into one. Your browser can only have so many connections to a website open at a time — given the overhead to set up each connection, it makes sense to combine several small scripts into a larger one.

But you don’t have to combine files manually! Use a script to merge the files — check out part 2 for an example script to do this. Giant files are difficult to edit – it’s nice to break your library into smaller components that can be combined later, just like you break up a C program into smaller modules.

Should I Gzip It?

Probably not. Although some browsers can accept compressed javascript (myfile.js.gz) or files returned with the “gzip” encoding header, this behavior is not consistent between browsers and can be problematic.

If you’re an expert, feel free to experiment, but for the majority of us I don’t think it’s worth the effort or potential headache.

All done? Keep learning.

Once you’ve performed the techniques above, recheck your page size using the tools above to see the before-and-after difference.

I’m not an expert on these methods — I’m learning as I go. Here are some additional references to dive in deeper:

The jQuery library, and virtually all of its plugins are constrainedwithin the jQuery namespace. As a general rule, “global” objects arestored inside the jQuery namespace as well, so you shouldn’t get a clashbetween jQuery and any other library (like Prototype, MooTools, or YUI).

That said, there is one caveat: By default, jQuery uses “$” as a shortcutfor “jQuery”[edit]Overriding the $-function

However, you can override that default by calling jQuery.noConflict() atany point after jQuery and the other library have both loaded. Forexample:

Finally, if you don’t want to define another alternative to the jQueryname (you really like to use $ and don’t care about using anotherlibrary’s $ method), then there’s still another solution for you. This ismost frequently used in the case where you still want the benefits ofreally short jQuery code, but don’t want to cause conflicts with otherlibraries.

This is probably the ideal solution for most of your code, consideringthat there’ll be less code that you’ll have to change, in order to achievecomplete compatibility.

Also see: Custom Alias[edit]Referencing Magic – Shortcuts for jQuery

If you don’t like typing the full “jQuery” all the time, there are somealternative shortcuts:

* Reassign jQuery to another shortcut o var $j = jQuery; o (This might be the best approach if you wish to use differentlibraries) * Use the following technique, which allows you to use $ inside of ablock of code without permanently overwriting $: o (function($) { /* some code that uses $ */ })(jQuery) o Note: If you use this technique, you will not be able to usePrototype methods inside this capsuled function that expect $ tobe Prototype’s $, so you’re making a choice to use only jQueryin that block. * Use the argument to the DOM ready event: o jQuery(function($) { /* some code that uses $ */ }); o Note: Again, inside that block you can’t use Prototype methods

Changing the features of the Popup

You can control the features of the popup using the last argument to the window.open method. The following code opens a window with a status bar and no extra features.window.open ("http://www.javascript-coder.com","mywindow","status=1");

The code below opens a window with toolbar and status bar.window.open ("http://www.javascript-coder.com","mywindow","status=1,toolbar=1");

The table shows the features and the string tokens you can use:

status

The status bar at the bottom of the window.

toolbar

The standard browser toolbar, with buttons such as Back and Forward.

location

The Location entry field where you enter the URL.

menubar

The menu bar of the window

directories

The standard browser directory buttons, such as What’s New and What’s Cool

resizable

Allow/Disallow the user to resize the window.

scrollbars

Enable the scrollbars if the document is bigger than the window

height

Specifies the height of the window in pixels. (example: height=’350′)

width

Specifies the width of the window in pixels.

ExamplesThe following code opens a window with menu bar. The window is resizable and is having 350 pixels width and 250 pixels height.window.open ("http://www.javascript-coder.com","mywindow","menubar=1,resizable=1,width=350,height=250"); Example 1

Moving the window to a desired location

You can use the window.moveTo function to move the popup window to a desired location.The code below shows positioning the popup at a desired location

function mypopup(){mywindow = window.open ("http://www.javascript-coder.com","mywindow","location=1,status=1,scrollbars=1,width=100,height=100");mywindow.moveTo(0,0);} The code positions the popup on the top left corner of the screen.

Putting it all together

Now we will combine all these information to create the popup windows of different types.The Code below opens a popup window when you enter the page:

All posted articles and comments are copyright by their owner, and reflect their own views and opinions, which may not necessarily be consistent with the views and opinions of the owners of the TheUnical Technologies.